Thermally expandable microspheres prepared from bio-based monomers

ABSTRACT

The present invention relates to thermally expandable microspheres at least partially prepared from bio-based monomers and to a process of their manufacture. The microspheres comprise a thermoplastic polymer shell encapsulating a blowing agent, wherein the thermoplastic polymer shell comprises a polymer being a homo- or copolymer of a lactone according to formula (1):wherein each of R1, R2, R3, R4, separately from one another, is selected from the group consisting of H and an alkyl group preferably with 1-4 carbon atoms. The invention further provides expanded microspheres, which can be used in a variety of applications.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 16/644,448,filed on Mar. 4, 2020, which is a U.S. National-Stage entry under 35U.S.C. § 371 based on International Application No. PCT/EP2018/073653,filed Sep. 4, 2018, which was published under PCT Article 21(2) andwhich claims priority to European Application No. 17189154.2, filed Sep.4, 2017, which are all hereby incorporated in their entirety byreference.

TECHNICAL FIELD

The present invention relates to thermally expandable microspheres atleast partially prepared from bio-based monomers and to a process oftheir manufacture. The invention further provides expanded microspheresprepared from the thermally expandable microspheres.

BACKGROUND ART

Thermally expandable microspheres are known in the art, as disclosed in,for example, U.S. Pat. No. 3,615,972 and WO 2007/091960. Thermallyexpandable microspheres comprise a shell of a thermoplastic resin and ablowing agent (propellant) encapsulated therein. Upon heating thethermoplastic shell softens and simultaneously the blowing agentvolatilizes while being retained within the thermoplastic shell, whichin turn causes an expansion of the thermally expandable thermoplasticmicrospheres to form expanded microspheres. Expandable microspheres aremarketed in various forms, e.g. as dry free-flowing particles, asaqueous slurry or as a partially dewatered wet cake.

Expandable microspheres can be produced by polymerizing ethylenicallyunsaturated monomers in the presence of a blowing agent. Conventionalmonomers used to form the polymer for the thermoplastic shell are amixture of vinyl containing monomers, such as, vinylidene chloride,acrylonitrile, methyl methacrylate, methyl acrylate, methacrylonitrileand methacrylic acid in various combinations. Conventional monomers areused as they impart thermoplastic properties to the thermoplastic shellensuring that the thermally expandable thermoplastic microspheres expandsatisfactorily when heated to form the expanded microspheres whilstretaining the blowing agent therein.

Conventional monomers are generally produced from petrochemicals whichoriginate from fossil fuels. Therefore, there is a growing need inpolymers produced at least partially from monomers obtained fromrenewable sources (bio-based monomers).

However, replacement of conventional monomers by bio-based monomers isnot easy because the bio-based monomers need to meet the demands of theconventional monomers and be compatible with these to form a polymer. Inorder to make expandable microspheres from the polymers there are evenmore requirements. First, the polymer must have the right surface energyto get a core-shell particle in a suspension polymerization reaction sothat the blowing agent is encapsulated. Second, the produced polymermust have good gas barrier properties to be able to retain the blowingagent. Finally, the polymer must have suitable viscoelastic propertiesabove glass transition temperature Tg so that the shell can be stretchedout during expansion. In addition, other objects, desirable features andcharacteristics will become apparent from the subsequent summary anddetailed description, and the appended claims, taken in conjunction withthe accompanying drawings and this background.

SUMMARY OF THE INVENTION

It has surprisingly been found that the above requirements are met whenthe polymer is at least partially produced from a certain group ofunsaturated lactones as a (co)monomer, and that it is possible to obtainthermally expandable microspheres with good expansion properties fromthe homo- and copolymers of these lactones.

Accordingly, the present invention provides, in a first aspect,thermally expandable microspheres comprising a thermoplastic polymershell encapsulating a blowing agent, wherein the thermoplastic polymershell comprises a polymer being a homo- or copolymer of a lactone withformula (1):

wherein each of R₁, R₂, R₃, R₄, separately from one another, is selectedfrom the group consisting of H and an alkyl group preferably with 1-4carbon atoms.

In a further aspect, the present invention relates to a process for themanufacture of thermally expandable microspheres comprising aqueoussuspension polymerization of ethylenically unsaturated monomer(s) usinga free-radical initiator in the presence of a blowing agent, wherein atleast one ethylenically unsaturated monomer is the lactone according toformula (1).

In a further aspect, the invention relates to expanded microspheresobtained by thermal expansion of the microspheres of the invention.

DESCRIPTION OF EMBODIMENTS

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by any theorypresented in the preceding background of the invention or the followingdetailed description.

The thermoplastic polymer shell of the microspheres according to theinvention comprises a homopolymer or a copolymer of the lactoneaccording to formula (1):

wherein each of R₁, R₂, R₃, R₄, separately from one another, is selectedfrom the group consisting of H and an alkyl group. The alkyl grouppreferably contains 1-4 carbon atoms. Particularly preferred alkylgroups are methyl and ethyl. More preferably, each of R₁, R₂, R₃, R₄,separately from one another, is selected from the group consisting of Hand CH₃.

In preferred embodiments, R₁, R₂, R₃, and R₄ in formula (1) are selectedas follows:

R₁═H, R₂═H, R₃═CH₃, R₄═H (α-methylene-γ-valerolactone (MVL), same asγ-methyl-α-methylene-γ-butyrolactone),

R₁═H, R₂═H, R₃═H, R₄═H (α-methylene-γ-butyrolactone (MBL)), R₁═CH₃,R₂═H, R₃═H, R₄═H (β-methyl-α-methylene-γ-butyrolactone (MMBL)), or

R₁═H, R₂═H, R₃═CH₃, R₄═CH₃ (γ,γ-dimethyl-α-methylene-γ-butyrolactone).

More preferably, the lactone is either MVL or MBL.

In some embodiments, the polymer is a homopolymer of the lactoneaccording to formula (1), which means there are no comonomers.

In other embodiments, the polymer is a copolymer of the lactoneaccording to formula (1) with other ethylenically unsaturated monomers.Preferably, the ethylenically unsaturated comonomers aremono-unsaturated. Suitable mono-unsaturated comonomers are for example(meth)acrylates; vinyl esters; styrenes such as styrene andα-methylstyrene; nitrile-containing monomers; (meth)acrylamides;vinylidene halides, vinyl chloride, vinyl bromide and other halogenatedvinyl compounds; vinyl ethers such as methyl vinyl ether, ethyl vinylether; N-substituted maleimides; dienes such as butadiene, isoprene andothers; vinyl pyridine; and any combination thereof.

Particularly preferred comonomers are selected from the list consistingof (meth)acrylonitrile, methyl (meth)acrylate, vinylidene chloride,methacrylic acid, methacrylamide or any combination thereof.

By “(meth)acrylate monomers” it is meant a compound and isomers thereofaccording to the general formula:

wherein R can be selected from the group consisting of hydrogen and analkyl containing from 1 to 12 carbon atoms and R′ can be selected fromthe group consisting of hydrogen and methyl. Examples of (meth)acrylatemonomers are acrylic acid and salts thereof, methacrylic acid and saltsthereof, acrylic anhydride, methacrylic anhydride, methyl acrylate,methyl methacrylate, ethyl acrylate, propyl acrylate, butyl acrylate,butyl methacrylate, propyl methacrylate, lauryl acrylate,2-ethylhexylacrylate, ethyl methacrylate, isobornyl methacrylate,hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, polyethyleneglycol (meth)acrylate. Preferred (meth)acrylate monomers include methylacrylate, methyl methacrylate and methacrylic acid.

By vinyl ester monomers it is meant a compound and isomers thereofaccording to the general formula:

wherein R can be selected from an alkyl containing from 1 to 17 carbonatoms. Preferred vinyl ester monomers are vinyl acetate, vinyl butyrate,vinyl stearate, vinyl laurate, vinyl myristate and vinyl propionate.

By nitrile containing monomers it is meant a compound and isomersthereof according to the general formula:

wherein R₁ and R₂ can be selected, separately from each other, from thegroup consisting of hydrogen and an alkyl containing from 1 to 17 carbonatoms, or a nitrile group.

Examples of nitrile containing monomers are acrylonitrile (R1═R2═H),methacrylonitrile (R1═CH3, R2═H), fumaronitrile (R1═CH3, R2═CN),crotonitrile (R1═CH3, R2═CH3). Preferred nitrile containing monomers areacrylonitrile and methacrylonitrile.

By (meth)acrylamide monomers it is meant a compound and isomers thereofaccording to the general formula:

wherein R₁, R₂ and R₃ can be selected, separately from each other, fromthe group consisting of hydrogen and an alkyl containing from 1 to 17carbon atoms or hydroxyalkyl.

Preferred (meth)acrylamide monomers are acrylamide (R1═R2═R3═H),methacrylamide (R1═CH3, R2═R3═H), and N-substituted (meth)acrylamidemonomers such as N,N-dimethylacrylamide (R1═H, R2═R3═CH3),N,N-dimethylmethacrylamide (R1═R2═R3═CH3), N-methylolacrylamide (R1═H,R2═H, R3═CH2OH).

By N-substituted maleimide monomers it is meant a compound according tothe general formula:

wherein R can be selected from an alkyl containing from 1 to 17 carbonatoms, or halogen atom.

Preferred N-substituted maleimide monomers are those where R is selectedfrom the group consisting of H, CH3, phenyl, cyclohexyl and halogen. Itis preferable that R is selected from the group consisting of phenyl andcyclohexyl.

In embodiments, at least one of the one or more ethylenicallyunsaturated comonomers is selected from (meth)acrylate monomers andnitrile-containing monomers. In further embodiments, at least onecomonomer is selected from acrylic acid, methacrylic acid,acrylonitrile, methacrylonitrile and C1-12 alkylacrylates andmethacrylates, for example those where the C1-12 alkyl group is methyl.

The lactone (co)polymer preferably contains at least 1 wt. % of thelactone, more preferably at least 10 wt. %, yet more preferably at least20 wt. % of the lactone based on the total weight of the polymer. Higheramounts of the lactone are also possible, such as at least 40 wt. %, orat least 50 wt. %, or at least 60 wt. %. In some embodiments, thelactone constitutes 75-100 wt. % of the (co)polymer, more preferably85-100 wt. % based on the total weight of the polymer. This allows tocreate microspheres with a high level of bio-based monomers including100% bio-based. In other embodiments, the copolymer contains less thanor equal to 50 wt % of the lactone, for example in the range of from 10to 50 wt %.

If present, the comonomers are preferably present in the lactonecopolymer in an amount of least 1 wt. %, or at least 10 wt. %, morepreferably at least 20 wt. % based on the total weight of the copolymer.In some embodiments, the comonomers may be present in a total amount ofat least 50 wt. %, or at least 60 wt. %, or at least 80 wt. % based onthe total weight of the copolymer. When a comonomer content in thepolymer is discussed within the present specification, it is understoodas the content of the comonomer as a building block in the copolymerrelative to the total polymer weight, and not as a free monomer contentof unreacted monomers that may be present in the polymer reactionproduct.

In some embodiments, it may be preferred that the lactone copolymercomprises at least one acidic monomer. An acidic monomer in this casecomprises both an ethylenically unsaturated bond and a carboxylic group.Examples of acidic monomers are (meth)acrylic acid, itaconic acid,maleic acid, fumaric acid and citraconic acid and their esters such asmonomethyl itaconate, monoethyl itaconate, monobutyl itaconate. Theacidic monomer can be present in amounts up to 70 wt. %, for example inamounts 1-50 wt. %, based on the total polymer weight.

In some embodiments, it may be preferred that the ethylenicallyunsaturated monomers are substantially free from vinyl aromaticmonomers. If included, the amount thereof is preferably less than 10 wt.%, more preferably less than 5 wt. %, most preferably less than 1 wt. %of the total polymer weight. Most preferably, the thermoplastic shellcopolymer is free from vinyl aromatic comonomers. An example of a vinylaromatic monomer is styrene.

In some embodiments, the ethylenically unsaturated monomers comprisesmall amounts of one or more crosslinking multifunctional monomers, suchas one or more of divinyl benzene, ethylene glycol di(meth)acrylate,di(ethylene glycol) di(meth)acrylate, triethylene glycoldi(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanedioldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glyceroldi(meth)acrylate, 1,3-butanediol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, 1,10-decanediol di(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol hexa(meth)acrylate, triallylformal tri(meth)acrylate,allyl methacrylate, trimethylolpropane tri(meth)acrylate, tributanedioldi(meth)acrylate, PEG #200 di(meth)acrylate, PEG #400 di(meth)acrylate,PEG #600 di(meth)acrylate, 3-acryloyloxyglycol monoacrylate, triacrylformal, triallyl isocyanate, triallyl isocyanurate, 1,4-butanedioldivinyl ether and trivinylcyclohexane or any combination thereof.Particularly preferred are crosslinking monomers that are at leasttri-functional. The amounts of crosslinking functional monomers may, forexample, be from 0.1 to 5 wt. % of the total polymer weight, morepreferably 0.1-3 wt. % and even more preferably 0.1-1 wt. %.

The softening temperature of the polymer shell, normally correspondingto its glass transition temperature (Tg), is preferably within the rangefrom 0 to 350° C., most preferably from 50 to 300° C.

The blowing agent (propellant) is selected such that it has asufficiently high vapour pressure at temperatures above the softeningtemperature of the thermoplastic shell to be able to expand themicroparticles. In most cases the boiling temperature of the blowingagent is not higher than the softening temperature of the thermoplasticshell. The boiling point at the atmospheric pressure of the blowingagent is preferably in the range from −50 to 250° C., more preferablyfrom −20 to 200° C., most preferably from −20 to 100° C. The amount ofthe blowing agent in the expandable microspheres is preferably from 5 to60 wt. %, more preferably from 10 to 50 wt. %, most preferably from 15to 40 wt. %, particularly most preferably from 15 to 35 wt. % based onthe total weight of the microparticles.

The blowing agent can be a single compound or a mixture of compounds.Preferably, the blowing agent is a hydrocarbon or a mixture ofhydrocarbons. More preferably, it is a hydrocarbon with 1 to 18 carbonatoms, even more preferably 3 to 12 carbon atoms, most preferably 4 to10 carbon atoms, or mixtures thereof. The hydrocarbons can be saturatedor unsaturated hydrocarbons. The hydrocarbons can be aliphatic, cyclicor aromatic hydrocarbons. Examples of suitable hydrocarbons includen-butane, isobutane n-pentane, isopentane, cyclopentane, neopentane,hexane, isohexane, neo-hexane, cyclohexane, heptane, isoheptane, octane,isooctane, decane, dodecane, isododecane and any combination thereof.Aside from them, other hydrocarbon types can also be used, such aspetroleum ether. It is preferable that the blowing agent containsn-butane, isobutane, n-pentane, isopentane, isohexane, isooctane,isododecane or mixtures thereof.

The temperature at which the expansion starts is called Tstart, whilethe temperature at which maximum expansion is reached is called Tmax. Insome applications it is desirable that the microspheres have a highTstart and high expansion capability, so as to be used in hightemperature applications like foaming of thermoplastic materials in e.g.extrusion or injection molding processes. Tstart for the expandablemicrospheres is preferably from 80 to 300° C., more preferably from 80to 250° C. In some embodiments, Tstart can be in the range from 190 to240° C. In other embodiments, lower Tstart temperatures are preferred,such as from 100 to 190° C. Tmax for the expandable microspheres ispreferably from 130 to 350° C., most preferably from 150 to 270° C.

The expandable microspheres preferably have a volume median diameterfrom 1 to 500 μm, more preferably from 3 to 200 μm, most preferably from3 to 100 μm.

The term expandable microspheres as used herein refers to expandablemicrospheres that have not previously been expanded, i.e. unexpandedexpandable microspheres.

The thermally expandable microspheres according to the present inventionhave a reduced eco-footprint as they are produced from monomers whichare at least partially bio-based. By bio-based it is meant that themonomers are not from a fossil fuel source. The lactones of formula (1)can be produced from biomass via different routes.α-Methylene-γ-butyrolactone (MBL), also known as Tulipalin A, is anaturally occurring substance that can be isolated from tulips. MBL,β-methyl-α-methylene-γ-butyrolactone (MMBL) andγ,γ-dimethyl-α-methylene-γ-butyrolactone can be synthesized frombio-based compounds such as itaconic acid which is produced byfermentation of different carbohydrates. α-Methylene-γ-valerolactone(MVL) can be derived from biomass via levulinic acid by a methoddeveloped by DuPont such as described in US 2006/100447.

The bio-based monomers used in the present invention surprisingly impartthermoplastic properties to the thermoplastic shell ensuring that thethermally expandable microspheres expand satisfactorily when heated toform expanded microspheres. The thermoplastic shell comprising thebio-based monomers surprisingly retains the blowing agent therein.

In a further aspect, the present invention relates to a process for themanufacture of thermally expandable microspheres as described above. Theprocess comprises aqueous suspension polymerization of ethylenicallyunsaturated monomers as described above using a free-radical initiatorin the presence of a blowing agent, wherein at least one ethylenicallyunsaturated monomer is the lactone according to formula (1) as describedabove. Regarding the kinds and amounts of the monomers and blowingagent, the above description of the expandable microspheres is referredto. The production may follow the same principles as described in U.S.Pat. Nos. 3,615,972, 3,945,956, 4,287,308, 5,536,756, EP 0 486 080, U.S.Pat. No. 6,509,384, WO 2004/072160, WO 2007/091960.

In a typical process of suspension polymerization, the monomer(s) andthe blowing agent are mixed together to form a so called oil-phase. Theoil-phase is then mixed with an aqueous mixture, for example bystirring, agitation, to form an emulsion. The emulsion formation allowsfor a manipulation of a size of the resultant emulsion droplets. It ispreferable that the emulsion droplets have a median diameter of up to500 μm and preferably in a range of 3-100 μm. The emulsion formation maybe performed by devices known in the art to provide emulsion dropletshaving a median diameter within the aforementioned range.

The emulsion may be stabilised with so called stabilising chemicals, orsuspending agents, as known in the art such as surfactants, polymers orparticles.

The preferred stabilisation system is particle stabilisation by aso-called “Pickering Emulsion” processes. The stabilisation of theemulsion droplets is preferred for a number of reasons; withoutstabilisation a coalescence of the emulsion droplets containing themonomers and the blowing agents may occur. Coalescence has negativeeffects; such as, a non-uniform emulsion droplet size distributionresulting in undesirable proportions of emulsion droplets with differentsizes, which in turn leads to undesirable properties of thermallyexpandable microspheres after polymerization. Furthermore, stabilisationprevents aggregation of thermally expandable microspheres. In addition,stabilisation may prevent formation of non-uniform thermally expandablemicrospheres and/or the formation of a non-uniform thermoplastic shelland an incomplete thermoplastic shell of the thermally expandablemicrospheres. The suspending agent is preferably present in an amountfrom 1 to 20 wt. % based on the total weight of the monomer(s).

In some embodiments, the suspending agent is selected from the groupconsisting of salts, oxides and hydroxides of metals like Ca, Mg, Ba,Zn, Ni and Mn, for example one or more of calcium phosphate, calciumcarbonate, magnesium hydroxide, magnesium oxide, barium sulphate,calcium oxalate, and hydroxides of zinc, nickel or manganese. Thesesuspending agents are suitably used at a high pH, preferably from 5 to12, most preferably from 6 to 10. Preferably magnesium hydroxide isused. Alkaline conditions however may facilitate the hydrolysis of thelactone (co)polymer and may in some cases be less preferred.

In other embodiments, it may be advantageous to work at a low pH,preferably from 1 to 6, most preferably from 3 to 5. A suitablesuspending agent for this pH range is selected from the group consistingof starch, methyl cellulose, hydroxypropyl methylcellulose,hydroxypropyl methylcellulose, carboxy methylcellulose, gum agar,silica, colloidal clays, oxide and hydroxide of aluminium or iron.Preferably silica is used.

In order to enhance the effect of the suspending agent, it is alsopossible to add small amounts of one or more co-stabilisers, for examplefrom 0.001 to 1 wt. % based on the total weight of the monomer(s).Co-stabilisers can be organic materials which can be selected, forexample, from one or more of water-soluble sulfonated polystyrenes,alginates, carboxymethylcellulose, tetramethyl ammonium hydroxide orchloride or water-soluble complex resinous amine condensation productssuch as the water-soluble condensation products of diethanolamine andadipic acid, the water-soluble condensation products of ethylene oxide,urea and formaldehyde, polyethylenimine, polyvinylalcohol,polyvinylpyrrolidone, polyvinylamine, amphoteric materials such asproteinaceous, materials like gelatin, glue, casein, albumin, glutin andthe like, non-ionic materials like methoxycellulose, ionic materialsnormally classed as emulsifiers, such as soaps, alkyl sulphates andsulfonates and long chain quaternary ammonium compounds.

In some embodiments, the suspending agent may be silica particles withco-stabilisers. The silica particles with co-stabilisers provide astabilising protective layer on a surface of the thermoplastic shell ofthe thermally expandable thermoplastic microspheres and the resultantexpanded microspheres. Such a combination of silica particles andco-stabilisers is disclosed in U.S. Pat. No. 3,615,972. Theco-stabilisers in this case can be selected from: metal ions (such asCr(III), Mg(II), Ca(II), Al(III) or Fe(III)); a flocculant (such as apoly-condensate oligomer of adipic acid and diethanol amine) withsometimes a reducing agent. The metal ions interact with the silicaparticles and the flocculants preventing coalescence of the emulsiondroplet and therefore stabilise the emulsion droplets. In otherembodiments, the silica particles may be modified with organosilanegroups as described in PCT/EP2017/067349.

In a suitable, preferably batch-wise, procedure for preparingmicrospheres of the invention the polymerization is conducted in areaction vessel as described below. For 100 parts of the monomer phase(suitably including the monomer(s) and the blowing agent, theproportions of which determine proportions of monomer(s) in the polymershell and the amount of blowing agent in the final product), one or morepolymerization initiator, preferably in an amount from 0.1 to 5 parts,aqueous phase, preferably in an amount from 100 to 800 parts, and one ormore suspending agent, preferably in an amount from 1 to 20 parts, aremixed and homogenised. The size of the droplets of the monomer phaseobtained determines the size of the final expandable microspheres inaccordance with the principles described in e.g. U.S. Pat. No.3,615,972, which can be applied for all similar production methods withvarious suspending agents. The suitable pH depends on the suspendingagent used, as described above.

The emulsion obtained is subjected to conventional radicalpolymerization using at least one initiator. Typically, the initiator isused in an amount from 0.1 to 5 wt. % based on the weight of the monomerphase. Conventional radical polymerization initiators are selected fromone or more of organic peroxides such as dialkyl peroxides, diacylperoxides, peroxy esters, peroxy dicarbonates, or azo compounds.Suitable initiators include dicetyl peroxydicarbonate,di(4-tert-butylcyclohexyl) peroxydicarbonate, dioctanyl peroxide,dibenzoyl peroxide, dilauroyl peroxide, didecanoyl peroxide, tert-butylperacetate, tert-butyl perlaurate, tert-butyl perbenzoate, tert-butylhydroperoxide, cumene hydroperoxide, cumene ethylperoxide,diisopropylhydroxy dicarboxylate, 2,2′-azo-bis(2,4-dimethylvaleronitrile), 2,2′-azobis(2-methylpropionate),2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] and the like. It isalso possible to initiate the polymerization with radiation, such ashigh energy ionising radiation, UV radiation in combination with aphotoinitiator or microwave-assisted initiation.

When the polymerization is essentially complete, microspheres arenormally obtained as an aqueous slurry or dispersion, which can be usedas such or dewatered by any conventional means, such as bed filtering,filter pressing, leaf filtering, rotary filtering, belt filtering orcentrifuging to obtain a so called wet cake. It is also possible to drythe microspheres by any conventional means, such as spray drying, shelfdrying, tunnel drying, rotary drying, drum drying, pneumatic drying,turbo shelf drying, disc drying or fluidised bed drying.

If appropriate, the microspheres may at any stage be treated to reducethe amount of residual unreacted monomers, for example by any of theprocedures described in the earlier mentioned WO 2004/072160 or U.S.Pat. No. 4,287,308.

A further aspect of the invention concerns expanded microspheresobtained by expanding expandable microspheres as described above. Theexpansion typically results in a particle diameter from 2 to 5 timeslarger than the diameter of the unexpanded microspheres. The density ofthe expanded microspheres may, for example, be from 0.005 to 0.06 g/cm3.The expansion is effected by heating the expandable microspheres at atemperature above Tstart, preferably at a temperature of at least 100°C. The upper temperature limit is set by when the microspheres startcollapsing and depends on the exact composition of the polymer shell andthe blowing agent. The ranges for the Tstart and Tmax can be used forfinding a suitable expansion temperature. In most cases a temperature inthe range 100 to 300° C., or more preferably in the range 150 to 250°C., is suitable. The density of the expanded microspheres can becontrolled by selecting temperature and time for the heating. Theexpansion can be effected by any suitable means for heating in anysuitable device, as described in e.g. EP 0 348 372, WO 2004/056549 or WO2006/009643.

The expandable and expanded microspheres of the invention are useful invarious applications such as printing inks (such as waterbome inks,solvent borne inks, plastisols, thermal printer paper, UV-curing inksetc. e.g. for textile, wall paper etc.), putties, sealants, toy-clays,underbody coatings, adhesives, debonding of adhesives, artificialleather, genuine leather, paint, non-woven materials, paper and board,coatings (e.g anti-slip coating etc.) for various materials such aspaper, board, plastics, metals and textile, explosives, cableinsulations, thermoplastics (such as polyethylene, polyvinyl chloride,poly(ethylene-vinylacetate), polypropylene, polyamides, poly(methylmethacrylate), polycarbonate, acrylonitrile-butadiene-styrene polymer,polylactic acid, polyoxymethylene, polyether ether ketone,polyetherimide, polyether sulfone, polystyrene andpolytetrafluoroethylene) or thermoplastic elastomers (such asstyrene-ethylene-butylene-styrene copolymer, styrene-butadiene-styrenecopolymer, thermoplastic polyurethanes and thermoplastic polyolefins),styrene-butadiene rubber, natural rubber, vulcanized rubber, siliconerubbers, thermosetting polymers (such as epoxies, polyurethanes andpolyesters). In some of these applications expanded microspheres areparticularly advantageous, such as in putties, sealants, toy-clays,genuine leather, paint, explosives, cable insulations, porous ceramics,and thermosetting polymers (like epoxies, polyurethanes and polyesters).In some cases it is also possible to use a mixture of expanded andexpandable microspheres of the invention, for example in underbodycoatings, silicone rubbers and light weight foams.

The invention will be further described in connection with the followingexamples which, however, are not to be interpreted to limit the scope ofthe invention. If not otherwise stated, all parts and percentages referto parts and percent by weight.

EXAMPLES

The expansion properties were evaluated on dry particles on a MettlerToledo TMA/SDTA851e with STARe software using a heating rate of 20°C./min and load (net.) of 0.06 N. Tstart is the temperature at which theexpansion starts, Tmax is the temperature at which maximum expansion isobtained and TMA density is the density of the microspheres at Tmax. Thelower the TMA density, the better the microspheres expand. The TMAdensity of 1 g/ml means no expansion.

The particle size and size distribution was determined by laser lightscattering on a Malvern Mastersizer Hydro 2000 SM apparatus on wetsamples. The median particle size is presented as the volume mediandiameter d(0.5).

The amount of the blowing agent was determined by thermal gravimetricanalysis (TGA) on a Mettler Toledo TGA/DSC 1 with STARe software. Allsamples were dried prior to analysis in order to exclude as muchmoisture as possible and if present also residual monomers. The analyseswere performed under an atmosphere of nitrogen using a heating rate at20° C. min⁻¹ starting at 30° C.

Example 1

A reaction mixture containing Mg(OH)2-stabilised organic droplets inwater was created by mixing the phases and stirring vigorously until asuitable droplet size had been achieved. The water dispersion contained3.4 parts of Mg(OH)2 and 284 parts of water. The organic dropletscontained 2.0 parts of dilauroyl peroxide, 27 parts of isopentane and0.3 parts of trimethylolpropane trimethacrylate. Acrylonitrile (AN) andα-methylene-γ-valerolactone (MVL) were added in the amounts as indicatedin Table 1 in parts per weight. Polymerization was performed at 62° C.in a sealed reactor under agitation during 20 hours. After cooling toroom temperature a sample of the obtained microsphere slurry was removedfor determination of the particle size distribution. After filtration,washing and drying the particles were analyzed by TMA. The dry particlescontained about 27 wt. % of isopentane and had a median particle size ofabout 74 μm. The TMA-results are found in Table 1.

Example 2

A dispersion comprising 242 parts of water, 30.7 parts of 50 wt. %surface-modified colloidal silica (Bindzil, 80 m2/g, particle size 32 nmsurface-modified with 50% propylsilyl/50% glycerolpropylsilyl) wasprepared and maintained at a pH of about 4.5. The aqueous dispersion wasmixed with an organic phase that contained 2.0 parts of dilauroylperoxide, 27 parts of isopentane and 0.3 parts of trimethylolpropanetrimethacrylate. Acrylonitrile (AN) and α-methylene-γ-valerolactone(MVL) were added in the amounts as indicated in Table 1. Polymerizationwas performed at 62° C. in a sealed reactor under agitation during 20hours. After cooling to room temperature a sample of the obtainedmicrosphere slurry was removed for determination of the particle sizedistribution. After filtration, washing and drying the particles wereanalyzed by TMA. The dry particles contained about 19 wt. % ofisopentane. The TMA-results and particle sizes are found in Table 1.

Examples 3-6

Microspheres were prepared in a plurality of polymerization experimentsperformed as in Example 2 except for monomers and hydrocarbon, whichwere added according to Table 1. The dry particles contained about 16-21wt. % of isooctane. The TMA-results and particle sizes are found inTable 1.

TABLE 1 MVL with AN TMA Composition Blowing Stab. Size T_(start) T_(max)density Ex Copolymer (parts) agent system (μm) (° C.) (° C.) (g/ml) 1MVL/AN 40/60 IP Mg(OH)₂ 74 155 199 0.016 2 MVL/AN 40/60 IP SiO₂ 5 169190 0.016 3 MVL/AN 55/45 IO SiO₂ 16 190 192 0.68 4 MVL/AN 70/30 IO SiO₂5 224 227 0.24 5 MVL/AN 85/15 IO SiO₂ 7 222 229 0.031 6 MVL/AN 100/0  IOSiO₂ 8 226 243 0.060 MVL = α-methylene-γ-valerolactone, AN =acrylonitrile, IP = isopentane, IO = isooctane

The choice of blowing agent (isopentane or isooctane) was dependent onthe Tg of the polymer, to better match the volatization of the blowingagent with the softening of the polymer shell. For lower Tstart ablowing agent with a lower boiling point (isopentane) was used and forhigher Tstart a blowing agent with a higher boiling point (isooctane)was used.

From Table 1 it can be seen that copolymers of MVL with AN withdifferent amounts can be used to prepare thermally expandablemicrospheres with good expansion properties such as low TMA density andhigh expansion temperature. The range 55-70% MVL seems to give less goodproperties although expansion is still possible. It may therefore beadvantageous to either use copolymers with the MVL content lower than 50wt. % or higher than 75 wt. % in the polymer, based on the total weightof the monomers. Polymers with 75-100 wt. % MVL are preferred since thisallows to prepare microspheres with a high level of bio-renewablemonomers, up to 100 wt. % (Example 6). An additional advantage ofpolymers with a high MVL content is the high starting expansiontemperature Tstart (>200° C.) as seen for Examples 4-6, which isparticularly suitable for high temperature end applications. High levelsof MVL correspond to low levels of comonomer AN.

Example 7

A reaction mixture containing Mg(OH)2-stabilised organic droplets inwater was created by mixing the phases and stirring vigorously until asuitable droplet size had been achieved. The water dispersion contained6.5 parts of Mg(OH)2 and 221 parts of water. The organic dropletscontained 0.52 parts of di(4-tert-butylcyclohexyl) peroxydicarbonate, 34parts of isopentane and 0.3 parts of trimethylolpropane trimethacrylate.Acrylonitrile (AN), α-methylene-γ-valerolactone (MVL) and methylmethacrylate (MMA) were added in the amounts as indicated in Table 2 inparts per weight. Polymerization was performed in a sealed reactor underagitation at 56° C. during 6 hours followed by 62° C. during 5 hours.After cooling to room temperature a sample of the obtained microsphereslurry was removed for determination of the particle size distribution.After filtration, washing and drying the particles were analyzed by TMA.The dry particles contained about 25 wt. % of isopentane and had amedian particle size of about 26 μm. The TMA-results are found in Table2.

Examples 8-10

Microspheres were prepared in a plurality of polymerization experimentsperformed as in Examples 1 except for monomers, which were addedaccording to Table 2. The dry particles contained about 17-24 wt. % ofisopentane. The TMA-results and particle sizes are found in Table 2.

Example 11

A reaction mixture containing Mg(OH)2-stabilised organic droplets inwater was created by mixing the phases and stirring vigorously until asuitable droplet size had been achieved. The water dispersion contained4.9 parts of Mg(OH)2 and 363 parts of water. The organic dropletscontained 2.0 parts of dilauroyl peroxide, 25 parts of isooctane and 0.4parts of trimethylolpropane trimethacrylate. α-Methylene-γ-valerolactone(MVL), methacrylamide (MAAM) and methacrylonitrile (MAN) were added inthe amounts as indicated in Table 2 in parts per weight. Polymerizationwas performed in a sealed reactor under agitation at 62° C. during 11hours followed by 80° C. during 4 hours. After cooling to roomtemperature a sample of the obtained microsphere slurry was removed fordetermination of the particle size distribution. After filtration,washing and drying the particles were analyzed by TMA. The dry particlescontained about 23 wt. % of isooctane and had a median particle size ofabout 74 μm. The TMA-results are found in Table 2.

Example 12

A dispersion comprising 259 parts of water, 8.6 parts of colloidalsilica (Bindzil 40 wt. %, particle size 12 nm), 60 parts of NaCl and 0.7parts of a poly-condensate oligomer of adipic acid and diethanol aminewas prepared and maintained at a pH of approximately 3.2. The aqueousdispersion was mixed with an organic phase that contained 2.0 parts ofdilauroyl peroxide, 27 parts of isopentane and 0.3 parts oftrimethylolpropane trimethacrylate. Acrylonitrile (AN),α-methylene-γ-valerolactone (MVL), methacrylonitrile (MAN), methylmethacrylate (MMA) and methacrylic acid (MAA) were added in the amountsas indicated in Table 2. 0.06 parts of Fe(NO3)3 was added and thepolymerization was performed at 62° C. in a sealed reactor underagitation during 20 hours. After cooling to room temperature a sample ofthe obtained microsphere slurry was removed for determination of theparticle size distribution. After filtration, washing and drying theparticles were analyzed by TMA. The dry particles contained about 24 wt.% of isopentane. The TMA-results and particle size are found in Table 2.

TABLE 2 MVL with AN and other comonomers TMA Composition Blowing Stab.Size T_(start) T_(max) density Ex Copolymer (parts) agent system (μm) (°C.) (° C.) (g/ml) 7 MVL/AN/ 20/60/20 IP Mg(OH)₂ 26 131 154 0.013 MMA 8MVL/AN/ 20/60/20 IP Mg(OH)₂ 70 113 176 0.011 MMA 9 MVL/AN/ 20/60/20 IPMg(OH)₂ 66 124 159 0.023 MA 10 MVL/AN/ 20/60/20 IP Mg(OH)₂ 51 122 2080.011 MAN 11 MVL/MAN/ 20/40/40 IO Mg(OH)₂ 74 191 234 0.0079 MAAM 12MVL/AN/ 20/17/17/20/26 IP SiO₂ 54 156 221 0.016 MAN/MMA/ MAA MVL =α-methylene-γ-valerolactone, AN = acrylonitrile, MAA = methacrylic acid,MAN = methacrylonitrile, MA = methyl acrylate, MMA = methylmethacrylate, MAAM = methacrylamide, IP = isopentane, IO = isooctane

From Table 2 it can be seen that copolymers of MVL with AN and othercomonomers can be used to prepare expandable microspheres with excellentexpansion properties such as low TMA density.

Examples 13-17

Microspheres were prepared in a plurality of polymerization experimentsperformed as in Example 11 except for monomers, which were addedaccording to Table 3. The dry particles of Examples 13-14 and Examples16-17 contained about 16-25 wt. % of isooctane. The dry particles ofExample 15 contained a high amount of isooctane (about 54 wt. %) whichplausibly can be explained by a low degree of polymerization whichresults in a relatively high level of isooctane compared to polymer. TheTMA-results and particle sizes are found in Table 3.

TABLE 3 MVL with MAN, MAAM, AN TMA Composition Blowing Stab. SizeT_(start) T_(max) density Ex Copolymer (parts) agent system (μm) (° C.)(° C.) (g/ml) 13 MAN/MAAM (ref) 50/50 IO Mg(OH)₂ 59 212 276 0.015 14MVL/MAN/MAAM 10/45/45 IO Mg(OH)₂ 69 202 259 0.0091 15 MVL/MAN/MAAM25/25/50 IO Mg(OH)₂ 73 212 228 0.15 16 MVL/MAN 50/50 IO Mg(OH)₂ 34 220225 0.017 17 MVL/MAAM 50/50 IO Mg(OH)₂ 65 See comment a) 18 MVL/AN/MAN30/45/25 IP Mg(OH)₂ 48 125 200 0.0097 19 MVL/AN/MAN 50/25/25 IP Mg(OH)₂54 153 196 0.027 a) Expansion is observed under microscope equipped witha heating stage. Several particles expanded between 160-250° C. MVL =α-methylene-γ-valerolactone, AN = acrylonitrile, MAN =methacrylonitrile, MAAM = methacrylamide, IP = isopentane, IO =isooctane

Example 13 is a comparative example wherein no lactone comonomers areused. Here a copolymer of methacrylonitrile and methacrylamide is used.

As can be seen, the microspheres according to the invention (Examples 11and 14-19) can be expanded at high temperature and have comparable orsome even better properties e.g. lower TMA density, compared to themicrospheres without bio-based monomers (Example 13).

Examples 18-19

Microspheres were prepared in a plurality of polymerization experimentsperformed as in Examples 1 except for monomers, which were addedaccording to Table 3. The dry particles contained about 24-28 wt. % ofisopentane. The TMA-results and particle sizes are found in Table 3.

Examples 20-24

Microspheres were prepared in a plurality of polymerization experimentsperformed as in Examples 1 except for acrylonitrile (AN),α-methylene-γ-butyrolactone (MBL), methacrylonitrile (MAN), methylmethacrylate (MMA) and methyl acrylate (MA) which were added in theamounts as indicated in Table 4. In Example 20 no trimethylolpropanetrimethacrylate was added while in Examples 21-24 trimethylolpropanetrimethacrylate was added according to Example 1. Blowing agents wereadded according to Table 4 in the same amounts as in Example 1. The dryparticles contained about 17-25 wt. % of hydrocarbon. The TMA-resultsand particle sizes are found in Table 4.

TABLE 4 MBL copolymers TMA Composition Blowing Stab. Size T_(start)T_(max) density Ex Copolymer (parts) agent system (μm) (° C.) (° C.)(g/ml) 20 MBL/AN 40/60 IP Mg(OH)₂   19 (a) 153 182 0.023 21 MBL/AN 40/60IO Mg(OH)₂ 45 173 189 0.053 22 MBL/AN/MMA 20/60/20 IP Mg(OH)₂ 37 109 1610.010 23 MBL/AN/MA 20/60/20 IP Mg(OH)₂ 40 114 156 0.033 24 MBL/AN/MAN20/60/20 IP Mg(OH)₂ 59 118 196 0.0074 (a) The particles had aggregatedso the size was estimated by optical microscopy MBL =α-methylene-γ-butyrolactone, AN = acrylonitrile, MAN =methacrylonitrile, MA = methyl acrylate, MMA = methyl methacrylate, IP =isopentane, IO = isooctane

Example 25

A dispersion comprising 246 parts of water, 26.8 parts of 50 wt. %surface-modified colloidal silica (Levasil, particle size 60 nmsurface-modified with 40% propylsilyl/60% glycerolpropylsilyl) wasprepared and maintained at a pH of approx. 4.5. The aqueous dispersionwas mixed with an organic phase that contained 2.0 parts of dilauroylperoxide, 27 parts of isopentane and 0.3 parts of trimethylolpropanetrimethacrylate. Acrylonitrile (AN) and α-methylene-γ-butyrolactone(MBL) were added in the amounts as indicated in Table 5. Polymerizationwas performed at 62° C. in a sealed reactor under agitation during 20hours. After cooling to room temperature a sample of the obtainedmicrosphere slurry was removed for determination of the particle sizedistribution. After filtration, washing and drying the particles wereanalysed by TMA. The dry particles contained about 17 wt. % ofisopentane. The TMA-results and particle sizes are found in Table 5.

Examples 26-30

Microspheres were prepared in a plurality of polymerization experimentsperformed as in Example 25 except for acrylonitrile (AN),α-methylene-γ-butyrolactone (MBL), methacrylonitrile (MAN), methylmethacrylate (MMA) and methyl acrylate (MA) which were added in theamounts as indicated in Table 5. Blowing agents were added according toTable 5 in the same amounts as in Example 25. The dry particles ofExamples 26-29 contained about 16-17 wt. % of isopentane while theparticles of Example 30 contained 5 wt. % of isooctane. The TMA-resultsand particle sizes are found in Table 5.

TABLE 5 MBL copolymers TMA Composition Blowing Stab. Size T_(start)T_(max) density Ex Copolymer (parts) agent system (μm) (° C.) (° C.)(g/ml) 25 MBL/AN 40/60 IP SiO₂ 24 150 185 0.038 26 MBL/AN/MMA 20/60/20IP SiO₂ 21 135 179 0.010 27 MBL/AN/MA 20/60/20 IP SiO₂ 27 124 164 0.01528 MBL/AN/MAN 20/60/20 IP SiO₂ 31 141 191 0.011 29 MBL/AN/MAN 50/32/18IP SiO₂ 27 147 201 0.013 30 MBL 100 IO SiO₂ 37 See comment a) a)Expansion is observed under microscope equipped with a heating stage. At180-200° C. a plurality of microspheres expanded about 4 times indiameter. MBL = α-methylene-γ-butyrolactone, AN = acrylonitrile, MAN =methacrylonitrile, MA = methyl acrylate, MMA = methyl methacrylate, IP =isopentane, IO = isooctane

The above examples show that it is possible to prepare thermallyexpandable microspheres from polymers largely based on bio-renewablelactone monomers. In some cases the polymer was prepared from 100%bio-based monomer MVL or MBL, which allows preparation of microsphereswith a 100% bio-based polymer shell. It is also possible to preparemicrospheres with a high expansion temperature—such as higher than 150°C., and some cases even higher than 190° C. or 200° C.

Examples 31-36 (Comparative)

An aqueous dispersion was prepared comprising 242 parts of water, 30.5parts of the Bindzil colloidal silica used in Example 2 (i.e. 80 m2/g,particle size 32 nm, surface-modified with 50% propylsilyl/50%glycerolpropylsilyl groups), 9.6 parts of 1M aqueous sodium hydroxide,and 15.3 parts of 10 wt % aqueous acetic acid. The aqueous dispersionwas mixed with an organic phase that contained 2.0 parts of dilauroylperoxide, 27 parts of isopentane and 0.3 parts of trimethylolpropanetrimethacrylate. Acrylonitrile (AN) and caprolactone (CL) were added inthe amounts as indicated in Table 6. Polymerization was performed at 62°C. in a sealed reactor under agitation during 20 hours. After cooling toroom temperature a sample of the obtained microsphere slurry was removedfor determination of the particle size distribution. After filtration,washing and drying the particles were analysed by TMA. The TMA-resultsand particle sizes are found in Table 6.

TABLE 6 Caprolactone copolymers Weight of TMA Monomer Blowing Stab. SizeT_(start) T_(max) density Ex Copolymer (parts) agent system (μm) (° C.)(° C.) (g/ml) 31 CL/AN 10/90 IP SiO₂ 28.7 20.8 54.4 >1 32 CL/AN 30/70 IPSiO₂ 24.0 21.2 53.7 >1 33 CL/AN 50/50 IP SiO₂ 18.1 21.6 66.9 >1 34 CL/AN70/30 IP SiO₂ 8.9 22.0 53.7 >1 35 CL/AN 85/15 IP SiO₂ a) a) a) >1 36CL/AN 95/5  IP SiO₂ a) a) a) >1 AN = acrylonitrile, CL = caprolactone,IP = isopentane a) No obvious formation of microspheres.

Caprolactone is a lactone, but does not fall within the scope of formula(1) above. The increased densities of the microspheres prepared usingcaprolactone are indicative of higher agglomeration of microspheres, andalso a lower yield of microspheres. The blowing agent content of thesamples was not measured, since the proportion of microspheres in thesample was extremely low.

These results demonstrate that, under corresponding synthesisconditions, its copolymers with acrylonitrile do not form expandablemicrospheres of sufficient quality or of sufficiently low density.

Examples 37-42 (Comparative)

The procedure used was identical to the procedure used for Examples31-36 above, except that the caprolactone was replaced with acorresponding weight of lactic acid (LA), in the amounts indicated inTable 7.

TABLE 7 Weight of TMA Monomer Blowing Stab. Size T_(start) T_(max)density Ex Copolymer (parts) agent system (μm) (° C.) (° C.) (g/ml) 37LA/AN 10/90 IP SiO₂ 26.3 21.6 53.8 >1 38 LA/AN 30/70 IP SiO₂ 22.2 34.472.1 >1 39 LA/AN 50/50 IP SiO₂ 6.6 20.4 65.4 >1 40 LA/AN 70/30 IP SiO₂5.2 21.5 55.7 >1 41 LA/AN 85/15 IP SiO₂ 2.7 21.8 40 >1 42 LA/AN 95/5  IPSiO₂ a) a) a) a) AN = acrylonitrile, LA = lactic acid, IP = isopentanea) No obvious formation of microspheres. Density not measured.

As with the caprolactone-containing examples, the densities were high(>1), indicating a high proportion of agglomeration, and the proportionof microspheres in the samples was extremely low. The amount of blowingagent in the samples was, therefore, not measured.

These results demonstrate that replacing the lactone of formula (1) withan alternative bio-based (co)monomer not of formula (1) does notnecessarily form expandable microspheres of sufficient quality or ofsufficiently low density under corresponding synthesis conditions.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of thevarious embodiments in any way. Rather, the foregoing detaileddescription will provide those skilled in the art with a convenient roadmap for implementing an exemplary embodiment as contemplated herein. Itbeing understood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope of the various embodiments as set forth in theappended claims.

What is claimed is:
 1. Thermally expandable microspheres having a sizeof from 1 to 100 microns, exhibiting a Tstart of from about 220° C. toabout 250° C., and comprising: a thermoplastic polymer shellencapsulating a blowing agent that is isopentane, isooctane, orcombinations thereof, wherein the thermoplastic polymer shell comprisesa copolymer of: α-methylene-γ-valerolactone (MVL) and/orα-methylene-γ-butyrolactone (MBL), and a co-monomer selected from thegroup consisting of acrylonitrile, methacrylonitrile, and combinationsthereof, wherein the weight percent of the α-methylene-γ-valerolactone(MVL) and/or the α-methylene-γ-butyrolactone (MBL) is from about 50 upto less than 100 parts by weight, and the weight of the co-monomer isfrom greater than zero up to about 50 by weight, each based on 100 partsby weight of the co-polymer.
 2. The microspheres according to claim 1having a particle size of from about 5 to about 34 microns.
 3. Themicrospheres according to claim 1 wherein the Tstart is from about 220°C. to about 226° C.
 4. The microspheres according to claim 1 wherein thecopolymer comprises the MVL that is present in a weight percent of fromabout 50 to about 70 parts by weight based on 100 parts by weight of theco-polymer.
 5. The microspheres according to claim 1 wherein thecopolymer comprises the MVL that is present in a weight percent of fromabout 50 to about 85 parts by weight based on 100 parts by weight of theco-polymer.
 6. The microspheres according to claim 1 wherein thecopolymer comprises the MVL that is present in a weight percent of fromabout 70 to about 85 parts by weight based on 100 parts by weight of theco-polymer.
 7. The microspheres according to claim 1 wherein thecopolymer comprises the MVL that is present in a weight percent of fromabout 70 to less than 100 parts by weight based on 100 parts by weightof the co-polymer.
 8. The microspheres according to claim 1 wherein thecopolymer comprises the MVL that is present in a weight percent of about50 parts by weight based on 100 parts by weight of the co-polymer andthe weight of the co-monomer is about 50 parts by weight based on 100parts by weight of the co-polymer.
 9. The microspheres according toclaim 1 wherein the copolymer comprises the MVL that is present in aweight percent of about 70 parts by weight based on 100 parts by weightof the co-polymer and the weight of the co-monomer is about 30 parts byweight based on 100 parts by weight of the co-polymer.
 10. Themicrospheres according to claim 1 wherein the copolymer comprises theMVL that is present in a weight percent of about 85 parts by weightbased on 100 parts by weight of the co-polymer and the weight of theco-monomer is about 15 parts by weight based on 100 parts by weight ofthe co-polymer.
 11. A process for the manufacture of the microspheresaccording to claim 1, comprising a step of polymerizing theα-methylene-γ-valerolactone (MVL) and/or the α-methylene-γ-butyrolactone(MBL) and the co-monomer to form the copolymer by aqueous suspensionpolymerization using a free-radical initiator in the presence of theblowing agent.
 12. The process according to claim 11, further comprisingthe step of stabilizing the suspension with SiO₂.
 13. A process forpreparing expanded microspheres comprising heating the thermallyexpandable microspheres according to claim 1 so that the thermallyexpandable microspheres expand.
 14. Expanded microspheres obtained bythermal expansion of the microspheres according to claim
 1. 15.Thermally expandable microspheres having a size of from about 5 to about34 microns, exhibiting a Tstart of from about 220° C. to about 226° C.,and comprising: a thermoplastic polymer shell encapsulating a blowingagent that is isopentane, isooctane, or combinations thereof, whereinthe thermoplastic polymer shell comprises a copolymer of:α-methylene-γ-valerolactone (MVL), and a co-monomer selected from thegroup consisting of acrylonitrile, methacrylonitrile, and combinationsthereof, wherein the weight percent of the α-methylene-γ-valerolactone(MVL) is from about 50 up to less than 100 parts by weight, and theweight of the co-monomer is from greater than zero up to about 50 partsby weight, each based on 100 parts by weight of the co-polymer.
 16. Themicrospheres according to claim 15 wherein the MVL is present in aweight percent of from about 50 to about 70 parts by weight based on 100parts by weight of the co-polymer.
 17. The microspheres according toclaim 15 wherein the MVL is present in a weight percent of from about 50to about 85 parts by weight based on 100 parts by weight of theco-polymer.
 18. The microspheres according to claim 15 wherein the MVLis present in a weight percent of from about 70 to about 85 parts byweight based on 100 parts by weight of the co-polymer.
 19. Themicrospheres according to claim 15 wherein the MVL is present in aweight percent of from about 70 to less than 100 parts by weight basedon 100 parts by weight of the co-polymer.
 20. Thermally expandablemicrospheres having a size of from about 5 to about 34 microns,exhibiting a Tstart of from about 220° C. to about 226° C., andcomprising: a thermoplastic polymer shell encapsulating a blowing agentthat is isooctane, wherein the thermoplastic polymer shell comprises acopolymer of: α-methylene-γ-valerolactone (MVL), and a co-monomerselected from the group consisting of acrylonitrile, methacrylonitrile,and combinations thereof, wherein the weight percent of theα-methylene-γ-valerolactone (MVL) is from about 50 up to less than 100parts by weight, and the weight of the co-monomer is from greater thanzero up to about 50 parts by weight, each based on 100 parts by weightof the co-polymer.